1. Field of the Invention
The invention relates generally to a continuously variable transmission including two pulleys each having a V-shaped groove with a variable width and an endless flexible member looped over the two pulleys, and more specifically to the structure of the continuously variable transmission.
2. Description of Related Art
There is a conventional continuously variable transmission including two pulleys each having a V-shaped groove with a variable width and an endless flexible member, such as a belt or a chain, which is looped over the two pulleys. Each of the pulleys has a pair of sheaves each having a tapered face, and the tapered faces of the sheaves are opposed to each other to define a V-shaped groove. The endless flexible member is looped over the two pulleys so as to be fitted in the V-shaped grooves of the pulleys. Thus, the rotation of one of the pulleys is transmitted to the other one of the pulleys via the endless flexible member.
By moving the sheaves in each pair relative to each other to vary the distance between the sheaves, the width of each V-shaped groove is varied. By varying the width of each V-shaped groove, the running radii of the circles of rotation of the endless flexible member looped over the pulleys are varied. As a result, the speed ratio between the two pulleys is varied. By allowing the relative distance between the sheaves in each pair to take a continuous value, the speed ratio between the two pulleys is continuously varied, that is, the speed ratio between the two pulleys is varied in a stepless manner.
Japanese Patent Application Publication No. 63-115966 (JP 63-115966 A) describes the pulley structure of a continuously variable transmission in which an endless flexible member (V-belt (3)) is used. The pulley structure includes a vibration suppression member (7) or (18) that is provided on a face of one of sheaves, the face being on the opposite side of the sheave from its tapered face, to suppress vibrations of the sheave (pulley half (4)) (refer to the description from line 16 in the lower left column to line 1 in the lower right column on page 2, and the description from line 9 to line 13 in the upper right column on page 4). The vibrations of the sheave are suppressed by the action of friction between the sheave and the vibration suppression member (refer to the description from line 13 to line 16 in lower right column on page 3 and the description from line 10 to line 16 in the lower left column on page 4). Note that the reference numerals within parentheses described above are used in JP 63-115966 A, and are not related to the reference numerals that will be used in the embodiments of the invention.
In the pulley structure described in JP 63-115966 A, when the sheave vibrates, there is a possibility that the amplitude of vibration at a portion of the sheave, on which a frictional force acts, will not be large and therefore a sufficient vibration damping effect will not be obtained.